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Warm

    Warm

    Vo1.13No.5Trans.NonfeITousMet.Soc.ChinaOct.2003 ;ArticleID:10036326(2003)05I18104

    ;Warmcompactionbehaviorsofiron-basedpowder ;lubricatedbydifferentkindsofgraphite?

    ;XIAOZhiyu(肖志瑜),LIYuan-yuan(李元元),NGAITungwaiLeo(倪东惠),

    ;GUOGuo-wen(郭国文),CHENWeiping(陈维平),

    ;(CollegeofMechanicalEngineering,SouthChinaUniversityofTechnology,Guangzhou510640,Chin

    a)

    ;Abstract:Warmcompactionbehaviorsandtheiraffectingfactorssuchascompactiontemperature,comp

    action

    ;pressureandlubricantconcentrationwerestudied.Effectofdiewalllubricationonthepowder’swalTncompaction

    ;behaviorwasa1sostudied.Theuseofsmallersizecolloidalgraphiteinvestigatedcangiveahighercompa

    ctdensity

    ;andlesserspring-backeffectthantheuseofflakegraphite. ;Keywords:warmcompactionbehavior;iron-basedpowdermetallurgy;springbackeffect ;CLCnumber:TF12

    ;1INTRoDUCTIoN

    ;Documentcode:A

    ;Conventionalpowdermetallurgy(PM)pro

    ;cessingcanproduceiron-basedPMpartswitha ;densitylessthan7.1g/cm.(arelativedensityof ;approximately900A).Theirmechanicalproperties ;aresubstantiallylessthanthoseoftheirfulldensi

    ;tycounterpart.Increasingdensityisthebestway ;toinereasetheperformanceofthePMparts. ;Therearemanyprocessesthatcanproduceiron- ;basedPMpartswithhighdensitysuchaspowder ;forging,doublepress/doublesinter(DP/DS)and ;Cuinfiltration,butwarmcompactionisthemost ;economicalandeffectiveway.Itscostisabout ;250AhigherthanthatoftheconventionalPM ;processbutabout40lowerthanthatofforging ;andabout10lowerthanthatofDP/DSandCu ;infiltrationc?.Casestudiesoneconomiccompeti

    ;tivenessofPMprocessingofgearcomponents ;showthat,withacomparablepartdensityandme

    ;chanicalproperties,comparedwithDP/DS,warm ;compactionhasaconsistentcostsavingoverthe

;entirerangeofproductionvolume.Withoutcom

    ;promisingpartperformance,conversiontowarm ;compactionfromDP/DS,a12costreductionfor ;planetarygearsandan89,6costreductionforsun ;gearswereachieved[.

    ;Literaturesfocusedonwarmcompactionwere ;firstlypublishedin1994E.’.Industrializationof

    ;thetechniquematuredinthemid1990’s.Withmi—

    ;normodificationontheconventionalPMequip

    ;ment.greencompactdensityof7.5g/cm.canbe ;obtainedbysinglepressing[?.Theonlydiffer

    ;encebetweenthewarmcompactionandthecon

    ;ventionalcompactionisthatthepowderhastobe ;treatedwithspeciallubricant,andthenthe ;wasraisedtothepre-settemperatureandarepressed ;inthedie.whichwasmaintainedatthe?rameompac-

    ;tiontemperaturewithadeviationof?2.7?[.

    ;Specialpowdermixforwarmcompactionisa

    ;vailableinworldmarket.InChina,CA0etalde

    ;velopedaseriesofiron-basepowderforwarmcom

    ;paction~?.

    ;Severalotherresearchersstudiedthe ;effectsofprocessmgparametersonthepropertms ;ofthesinterediron-basealloysandstudiedthe ;densifieationmechanismofwarmcompaction[.?.

    ;Someresearchersstudiedwarmcompactionroute ;toprepareparticulatereinforcediron-basedmateri

    ;als[12t.LIetalstudiedtheeffectofdiewalllu

    ;brieationonthewarmcompaction[.’..However,

    ;noliteraturereportedtheeffectofdifferentkinds ;ofgraphiteonthewarmcompactionbehaviorof ;theironbasedpowder.Theaimofthispaperisto ;studywarmcompactionbehaviorsofiron-based ;powdersandtocomparetheresultswiththoseof ;conventionalcoldcompaction.

    ;2EXPERIMENTAL

    ;Highpuritywateratomizedironpowderwith ;anaverageparticlesizeof75pmwasusedasraw ;materia1.Somecharacteristicsoftheironpowder ;?Foundationitem:Project(50135020)supportedbytheNationalNaturalScienceFoundationofChina;proj

    ect(2001AA337010)supported

    ;bvtheNationa1AdvancedMaterialsCommitteeofChina;project([2OO2]N0.77)supportedbytheMaj

    orinScienceandTechnologyRe_

;searchofEducationMinistryofChina;project(003019)supportbytheNaturalScienceFoundationofGu

    angdongProvince,China;proiect

    ;([2002]No.43)supportedbyGuangzhouScienceandTechnologyBreakthroughProject

    ;Receiveddate:20021130;Accepteddate:20030208

    ;Correspondence:XIAOZhi-yu,PhD;Tel:+862087111983;E-mail:XZY1221mail@21cn.com

    ;——一『1]I??—I]

    ;

    ;?1182?Trans.NonferrousMet.Soc.Chinaoct.2003 ;Table1Chemicalcompositionandpropertyofironpowder ;usedinthisstudyarelistedinTable1.Powdersof ;carbonylNi(3-5m),electrolyticCu(<75m), ;reducedMo(<75m)andpowderofflakegraph

    ;ite(<75ttm)orcolloidalgraphite(23m)were

    ;usedasalloyingelements.Thecompositionofthe ;mixedpowderinmasswas2.0Cu,2.0Ni,1. ;OMoand0.6-1.0C.Unlessspeciallymen

    ;tioned,allcompositions

    ;throughoutthispaper.

    ;werereportedinmass

    ;Additional0.25and

    ;0.6ofpolymericlubricantweremixedwiththe ;powderfordiewalllubricatedandnon-diewalllu

    ;bricatedexperiment,respectively.Thepowder ;wasmixedinarotarymixingmachinefor1h.Ap- ;proximately29ofthemixedpowderwasraisedto ;theassignedtemperatureinamold,whichwas ;heatedbyaresistantcoil.Thepowderwaswarmly ;compactedintostandardtensiletestbars(GB7963- ;1987)orcylinderswithdiameterof12mmand ;heightof7mmatatemperaturerangingfromam

    ;bienttemperatureto16O.C,andwithapressure ;rangingfrom500to800MVainaheatedsteelmold. ;Forthediewalllubricatedcase.emulsifiedpolytet

    ;rafluoroethylene(PTFE)was

    ;wallforlubrication.Green

    ;effectweremeasured.

    ;brushedontheinnerdie

    ;densityandspring-back

    ;Spring-backeffectwasdeterminedbymeasur

    ;ingthedifferencebetweenthesizeofthesample ;andtheinnersizeofthedie.Thesamplesize ;changeafterejectionwasmeasuredbymicrometer ;accordingtoGB/T51591985.Sizechangepercent

;age(Adm)isdefinedas:

    ;?DG[(GdD)/dD]x100

    ;wheredGanddDarethesizeofthegreencompact ;andtheinnersizeofthedie,respectively. ;3RESUI1

    ;Fig.1showstherelationshipbetweenthe ;greencompactdensityandthecompactpressure ;forconventionalcompaction,warmcompactionand ;diewalllubricatedwarmcompaction.Theyall ;showanincreasewithincreasingthepressure. ;Effectofcompactingtemperatureongreendensity ;ismoreobviousforcompactionwithhigherpres

    ;sure.Comparedwiththeconventionalcompaction, ;thereisanincreaseof0.19g/cm.at800MPaand ;anincreaseof0.1g/cm.at500MPabyusingwarm ;compaction.Anincreaseof0.25g/cm.canbeob

    ;tainedifdiewalllubricatedwarmcompactionis ;used.

    ;Fig.2showstherelationshipbetweenthe ;Compactpmssure/MPa

    ;Fig.1Relationshipbetweengreen

    ;densityandcompactpressureforconventional ;compaction,warmcompactionanddie

    ;walllubricatedwarmcompaction.

    ;7.40

    ;7.35

    ;7-3O

    ;7.25

    ;7.2O

    ;7.15

    ;7.1O

    ;7.O5

    ;2O6Oloo140180

    ;Compacttemperatum/’C

    ;Fig.2Relationshipbetweengreen

    ;densityandcompacttemperaturefor

    ;warmcompactionanddiewalllubricated ;warmcompactionsamples

    ;greendensityandthecompacttemperaturefor ;warmcompactionanddiewalllubricatedwalTl-i ;compactionsamples.FromFig.2,itisseenthat ;greendensitiesincreasewiththeincreaseoftern

    ;peratureuntilthetemperaturereached120?.

    ;thendecreasegradually.Fordiewalllubricated

    ;warmcompaction,thecompactdensityseemsto ;decreaseatahighertemperature.

    ;Fig.3showstherelationshipbetweenthe ;greendensityandthecompactpressureforwarm ;compactedsamplelubricatedbydifferentkindsof ;graphite.Theyallshowanearlylinearincrease ;—n.IIu.?\?=luI10ugu.昱一lsQ=l譬暑0u

    ;

    ;Vo1.13?.5Warmcompactionbehaviorsofiron—basedpowderlubricatedbygraphite.1183.

    ;7.3l

    ;7.27

    ;7.23

    ;7.19

    ;7.15

    ;500550600650700750

    ;Compactprcssure/MPa

    ;Fig.3Relationshipbetweengreen

    ;densityandcompactpressureforwarm

    ;compactedsamplelubricatedbydifferent ;kindsofgraphite

    ;withtheincreaseopressure.Theuseofcolloidal ;graphitecangiveflhighergreendensity.Forcol

    ;loidalgraphitethereexistsanoptimalgraphitecon

    ;tenttoobtainhighercompactdensity,theoptimal ;contentinthisstudyis0.8.

    ;Fig.4showstherelationshipbetweenthe ;springbackeffectandthecompactpressurefor ;warmcompactedsamplelubricatedbydifferent ;kindsofgraphite.FromFig.4,itcanbeseenthat ;springbackeffectofallsamplesincreaseswiththe ;increaseofpressure.Compactslubricatedbycol

    ;loidalgraphiteshowlesserspringbackeffect.At

    ;highpressurethespringbackeffectsondiewall

    ;lubricatedandnondiewalllubricatedwarmcom

    ;pactionsamplesaresimilar,butatlowerpressure ;thediewalllubricatedwarmcompactionsamples ;showlargerspring-backeffect.

    ;Fig.5showstherelationshipbetweenthe ;springbackeffectandthegreendensityforwarm ;compactedsampleswithdifferentcarboncontents ;lubricatedbycolloidalgraphite.Theyallshowan ;increasewiththeincreaseofdensity. ;4DIsCUSSIoN

    ;Theintroductionofdiewalllubricationen

    ;hancestheeffectivepressurethatexertsonthe ;powderduringthecompaction.Theshapesofthe ;diewalllubricatedandnondiewalllubricated

    ;curvesinFig.1aresimilar.withthediewalllubri

    ;catedcurveshiftedupward.Thissimilarityin ;shapeindicatesthatthedensificationmechanism ;remainsunchangedeventhediewallisbeinglubri

    ;cated.Themaximumgreendensitycanbeobtained ;at120?becausethelubricantusedinthisstudy ;meltsapproximatelyat120?.Ashavingbeen

    ;pointedoutbyLIetalc.thedecreaseof ;lubricant’sfrictioncoefficientwiththeincreaseof

    ;0.32

    ;0.28

    ;0.24

    ;0.20

    ;0.16

    ;0.12

    ;5005506006507007508oo

    ;Compactpressure]MPa

    ;Fig.4Relationshipbetweenspring-back ;effectandcompactpressureforwarm

    ;compactedsamplelubricatedbydifferent ;kindsofgraphite

    ;0.24

    ;0.22

    ;0.20

    ;0.18

    ;0.16

    ;0.14

    ;0.12

    ;0.10

    ;7.157.207.257.307-357.40

    ;Compactdensity/(g?enl-3)

    ;Fig.5Relationshipbetweenspringback

    ;effectandgreendensityforwarm

    ;compactedsampleswithdifferent

    ;carboncontentsusingcolloidalgraphite ;temperatureisthemainreasontoobtainhigher ;greendensityatelevatedcompactiontemperature. ;Themeltedlubricantspreadoutinthecompactand ;modifiedthelubricatingconditionfurtherduring ;thecompaction.Whenthetemperatureexceeded ;themeltingtemperature,effectsofthelubricant

    ;diminishandthegreendensitydecreasesaccording- ;ly.Fordiewalllubricatedwarmcompactionthe ;highmeltingpointofPTFEcanincreasetheeffec- ;tivepressurewellbeyond120?.

    ;Graphiteisaneffectivesolidlubricant.Ithas ;flhighelasticmodulus.Whenthecompressstress ;releasesafterejectionfromthedie,graphiteparti- ;cleswillatleastpartiallyrecoverfromitscompres

    ;sivestateandthusreducesthecompact’sdensity.

    ;Thesizeofcolloidalgraphiteisabout1Izoofflake ;graphitehas.Theycanevenlyfillintheinter

    ;spacesinsidethecompact.Therecoveringofthe ;compactedgraphiteisthereforecompensatedby ;…fI-I1

    ;l.Q)I譬口口?

    ;g0)/?Qp1口昌0u

    ;l}/00Q)Iq日口口?

    ;

    ;?1184?Trans.NonferrousMet.Soc.Chinaoct.2003 ;theavailablespaceandthusreducesthespring

    ;backeffect,whilecompactscontainingflake ;graphiteshowlargerspring-backeffectsinceits ;largesizestopsitfromfillingtheinterspaces. ;Therefore,thehighflakegraphitecontentwillde- ;creasethecompact’sdensity.Forcolloidalgraph—

    ;ite,sincethereareinterspacesthatcancompen

    ;satetheelasticrecoveringofthegraphiteparticles, ;thereexistsanoptimalgraphitecontenttoobtain ;thehighestcompactdensity.Theoptimalcontentis ;0.8inthestudy,asshowninFig.3.

    ;Nomatterflakeorcolloida1graphiteisused. ;itignorestheCcontentinthecompact,andallthe ;curvesshowninFig.4havesimilarslopesexcept ;forthediewalllubricatedcurve.whichexhibitsa ;gentleslope.Comparedwiththenondiewalllu

    ;bricatedsample,whichalsocontains0.8%colloi

    ;dalgraphite.diewalllubricatedsampleshows ;strongerspring-backeffectatcompactionpressure ;lowerthan700MPaandhasalesserspringback

    ;effectatcompactionpressurehigherthan700 ;MPa.Themajorfunctionfordiewalllubricantis ;toreducethefrictionbetweenthediewallandthe ;powderparticles(orgreencompact).Itcanan

    ;hancetheeffectivepressurethatexertsonthe

    ;powderduringthecompaction.Itcanbeexpected ;thatthediewalllubricatedcasewillshiftthe ;curvestotherightsideinFig.4.

    ;Thehigherthedensityis,thelargerthe ;spring-backeffectis,nomatterflakeorcolloidal ;graphiteisused.Thehigherdensityimpliesthe ;lessertheavailableinterspacesinthecompact,the

    ;largertheenergystoredintheseverelydeformed ;powderparticles.Thestoredelasticenergywillbe ;releasedoncethecompactisejectedoutfromthe ;die,leadingtotheexpansionofthecompact. ;5CoNCLUSIoNS

    ;Thediewalllubrieated

    ;lubricatedwarmcompaction

    ;andthenondiewall

    ;havethesamedensifi

    ;cationmechanism.Inthisstudy,themaximum ;greendensitycanbeobtainedat120?.Fordie

    ;walllubricatedwarmcompactionPTFE.thehigh ;meltingpointcanmcreasetheeffectivepressure ;wellabove12O?.Theuseofsmallersizecolloidal ;graphitecangiveahighercompactdensitythan ;thatflakegraphitecan.Nomattercolloidalor ;flakegraphiteisused,springbackeffectincreases

    ;withtheincreaseofcompactionpressure.Com

    ;pactsusingcolloidalgraphiteshowlesserspring

    ;backeffect.Athighpressure,thespring-back ;effectforbothdiewalllubricatedandnondiewall

    ;lubricatedwarmcompactionsamplesareapproxi- ;matelythesame,butatlowerpressure,thedie ;walllubricatedwarmcompactionsamplesshows ;largerspringbackeffect.

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    ;(EditedbyLIXim~-qu)

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